1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device substrate, and particularly to a method for fabricating an pixel array substrate.
2. Description of Related Art
Along with the development of telecommunication and video technology, many kinds of displays are widely used in cell phones, notebook computers, digital cameras, personal digital assistants (PDAs) or the like. Among such displays, liquid crystal displays (LCDs) and organic light emitting diode (OLED) displays having advantages such as light weight, slimness and low power consumption, have become a mainstream of the display market. Fabricating a pixel array substrate with a semiconductor process is necessary for an LCD or an OLED display. Images can be produced on the display by correspondingly adjusting the colors displayed in different pixels of the pixel array substrate.
FIG. 1 is a top view of a part of a conventional pixel array substrate, while FIGS. 2A to 2E are cross-sectional views (along line A-A′ shown in FIG. 1) illustrating a step flow for fabricating a pixel array substrate as shown in FIG. 1. Referring to FIG. 1, a conventional pixel array substrate 100 includes a substrate 110, a plurality of thin film transistors (TFTs) 120, a plurality of scan lines 130, a plurality of data lines 140, and a plurality of pixel electrodes 150. The TFTs 120 are disposed on the substrate 110, and each of the TFTs 120 includes a gate electrode 122, a source electrode 124 and a drain electrode 126, electrically connected to the corresponding scan line 130, data line 140 and pixel electrode 150, respectively. The scan lines 130 and the data lines 140 are generally alternately configured in columns and rows, thus defining a plurality of pixel units (not shown). Specifically, the scan lines 130 are disposed in rows, and the data lines 140 are disposed in columns, while the TFTs 120 are configured near the intersections of the scan lines 130 and the data lines 140.
The TFTs 120 are controlled to be switched on or off in accordance with scanning signals provided by the scan lines 130. When a TFT 120 is turn-on, a corresponding pixel electrode 150 can receive data signals from a corresponding data line 140 via the TFT 120. Thus, the corresponding pixel can adjust the corresponding color to be displayed. However, limited by the conventional process, a thickness of the data lines 140 is usually smaller than a thickness of the scan lines 130, in such a way, a sheet resistance of the data lines 140 is greater than a sheet resistance of the scan lines 130. As such, a delay of data signal transmit will occur, which decreases display quality of the pixel array substrate 100. Particularly, larger pixel array substrates are become more popular; if the pixel array substrate has a larger size, the delay would be even more serious.
The process for fabricating such a pixel array substrate 100 is described below. Referring to FIG. 2A, a first optical mask process is conducted to form a gate electrode 122 on a substrate 110, and scan lines 130, as shown in FIG. 1, are formed at the same time. Then, referring to FIG. 2B, a dielectric layer 160 is formed over the substrate 100 to cover the gate electrode 122, and after that a second optical mask process is conducted to form a channel 128 over the gate electrode 122. Referring to FIG. 2C, a third optical mask process is conducted to form a source electrode 124, a drain electrode 126 and a data line 140; the gate electrode 122, the source electrode 124, the drain electrode 126 and the channel 128 as a whole constitute a TFT 120. Referring to FIG. 2D, a protecting layer 170 is then formed to cover the TFT 120, and thereafter a fourth optical mask process is conducted to define a contact window 172 in the protecting layer 170 for exposing a part of the drain electrode 126. Referring to FIGS. 1 and 2E, a fifth optical mask process is finally conducted to form a pixel electrode 150 on the protecting layer 170, in which a part of the pixel electrode 150 is filled into the contact window 172, so that the pixel electrode 150 is electrically connected to the drain electrode 126. Up to now, a pixel array substrate 100 as shown in FIG. 1 is fabricated.
The cost for making optical masks is one of the considerable expenses for fabricating such a pixel array substrate 100. Unfortunately, according to the above-illustrated process, five different optical masks are required for fabricating such a pixel array substrate 100. Therefore, it is hard to reduce production cost addressing to such a process. Particularly, when a larger pixel array substrate 100 is to be fabricated, larger optical masks are correspondingly required, thus the production cost has to be further increased.